When an electric actuator beginning with a linear actuator such as a reciprocating motor is electrically driven, there is the possibility that collision of a movable element with a stator, breakage of a controller by flowing of current or application of a voltage which exceeds an acceptable current or voltage through or to the controller or the like may occur. Collision of the movable element with the stator gives rise to generation of noise, generation of abnormal vibration and degradation of the life time, and breakage of the controller gives rise to burnout of the device. Thus, both of the collision and the breakage must be prevented.
As a countermeasure against the collision and the breakage, a technique of limiting (clamping) current or a voltage of a driving instruction signal which is a periodical signal for the instruction of driving of an electric actuator and carrying out a process against the abnormality before a failure occurs is considered as an effective method.
For example, an apparatus shown in FIG. 20 of Patent Document 1 includes an instruction value production section for receiving an engine speed and so forth as inputs thereto to determine and output an amplitude instruction value and a frequency instruction value of vibration to be generated by excitation means which is an electric actuator by arithmetic operation, an amplitude upper limit clamp table in which an upper limit of an applicable current value which is determined from the amplitude instruction value and the frequency instruction value outputted from the instruction value production section, and an application current production section. The application current production section receives the amplitude instruction value and the frequency instruction value as inputs thereto and refers to the amplitude upper limit clamp table to carry out correction for limiting the inputted amplitude instruction value to a value within a suitable (movable) range, and determines and outputs an instruction value of current to be applied to excitation means, for which a reciprocating motor is used, based on the inputted frequency instruction value and the amplitude instruction value after the correction (limitation). Then, by usually driving the movable element of the linear actuator within a suitable movable range, collision with a stopper can be avoided and generation of collision noise can be suppressed.
Further, a motor current instruction is in most cases formed by superposition of several elements, and, in this instance, the sum total value of them is used as a vibration damping current instruction value.
For example, in an apparatus shown in FIG. 10 of Patent Document 1, a line after the engine speed and so forth are inputted until a current instruction value is outputted is provided for each of a primary (fundamental order) vibration mode and a secondary (high order) vibration mode, and the sum total of the current instruction values is inputted as a superposition current instruction to the reciprocating motor.